Various types of semiconductor devices are proposed to improve characteristics of rectifying semiconductor devices. For example, there is proposed a method of reducing an electric field in corner portions of a trench bottom portion of a semiconductor device by implanting ions into the entire trench bottom portion (for example, see Patent Document 1). The withstand voltage of the semiconductor device can be improved by arranging a region for reducing an electric field (hereafter, referred to as “electric field reducing region”) in the trench bottom portion.